Method for secondary recovery of petroleum



R aazasesaua United States Patent 0 wet reservoir. This means that in the case of reservoirs 3,386,506 having their wettability reversed, more oil can be dis- METHOD FOR SECONDARY RECOVERY OF PETROLEUM ice placed when such step is followed by gas-water injection. It is an object of my invention to provide a method for Robert J. Quance, Tulsa, Okla, assignor to Pan American 0v 0 l e lo multa ousl or alternatel lrsetlroleunn Corporation, Tulsa, 62:121., a corporation of 5 2 2 3235 3 2 gg gigi z gg andyfluid e g g e aware No Drawing. Filed Apr. 3, 1966, Ser. No. 541,126 Water, injection flooding operations. It is another ob ect 11 Claims, (Cl. 166-9) of my mvention to provide a method for obtairnng substantially more oil than is possible by the application of a wettability reversal flood alone or a flooding operation using gas-water, or other suitable drive agents. It is a ABSTRACT OF THE DISCLOSURE further object of my invention to provide means for im- Residual oil saturations obtained by waterflooding in proving the sweep efiiciency, i.e., the mobility ratio, of a the presence of a gas phase are lower than those obtained wettability reversal flood by simultaneously or alternately in the absence of gas, and reduction in oil saturation is 15 injecting gas into the formation along with the wettability appreciably more for a water-wet reservoir. It is reasoned reversal component. It is still another object of my inventhat the combination of the two would increase oil recovtion to provide a method for the increased recovery of ery. In addition, in'ection of gas with water tends to impetroleum from an underground deposit thereof by first 1 J I e 0 l e s prove the mobility ratio and give better areal and vertlcal introducing an aqueous solution having dissolved therein sweep efliciency. The injection of gas and water may be a chemical capable of reversing the wettability of an oilalternately done. bearing formation, said solution being accompanied by the simultaneous or alternative injection of gas after which a driving fluid such as water is introduced and The present invention relates to an improved method 9 be accompaliied by simulianeous or r from saturates": as; 22323523.???iihfihii; thereof' Morehp grtflcularly It IS concernid secondary ratio of a wettability reversal flood bank by introducin recovery met 0 or recovering petro eum rom a reservoir thereof wherein the wettability of said reservoir is igi i g g ig bani; S of gas pnor to altered and the oil is produced thereafter by means of 1 .3 523 s z l i al g i d injection of a suitable drive agent. e 1 1 y 0 mg use The recovery of petroleum from reservoirs thereof by description refers to the in ection of certain chemicals which ac to alter the wettabilit of a neutr or il-w means of various typis of fioodmg Operauons have long reservoir in the direction of beiiig more wai eir Wei Tli: tbeen regardeddas i seconigary recovgry i mechanism involved is to release some of the oil within 0 secure goo o1 isp acement e ciencies. ne 0 t e a rocks pore structure by mcreasing the rocks surface prmclp a1 drawbacks of Such proceduries h area actually Wet by the wettability agent or the chosen been he arge amqunt of unrecovered O11 typ 103.1 of dnves water which is used to drive the chemical bank through g g g fg gfi gg? LE g j g z g i g fig the reservoir. While an increased water-Wet condition is achieved in a wettabilit reversal flood on either neutral SP eakmg the 1m proved reciwery methqds have larger 40 or oil-wet reservoirs this merely implies more of the Y i and larger Olleratmg cost.wh.lch have tended t0 rock is being Wet wiih Water This serves to liberate oil l1m1t the extent of their field appllcation. Currently, irnfwrn the rocks pore surface's and permits more on to Secondary recgvery techmque? Involve Wettablhty be displaced. While the normal use of wettability reversal .ir floodmg f0 lowed by l i Watgrfloodmg' flooding is for oil-wet reservoirs, it can be applied just as us, after 15-20 percent of the Oil in place has been wento reservoirs of neutralwettabflity recovered by y h Waterfloodmg usually can In carrying out the process of my invention and after account for mcreasmg thls {recovery up to 3040 establishing that the reservoir involved is oil wet, as decent.Although the waterfi9dmg procfiss represents a termined by the methods outlined in US. 3 028 912 and/ i i advance Over Prevlously PYaFmed methodsfnany or 3,203,480, an aqueous slug of a suitable wettability mllhoni barrels of recoverable o11WOu1d1?e1efl.mthe reversal chemical is introduced into the formation toreservoirs if such process represented the ultimate in secuether with a volume of gas or if preferred alternate ondary recovery techniques.

slugs of the chemlcal bank and gas may be ln ected. By g g 332 l fiz gg g g ggii i gggg ggggg & this technique the mobility ratio is considerably improved, b b d h b y O resulting in improved vertical as Well as areal sweep efi g 0 i w an 01 x iifi 3.5. ficiencies of the chemical bank. Alternatively, and pars r S {or f; g i ticularly Where the reservoir has rather Wide variations U S 5 2 6 6 :2 33 2 g 532 33 in permeability, it is desirable to inject a slug of gas, i.e.,

a n .f not more than about 10 percent of the pore volume to disclose various additives sultable for use as wettabilny be flooded prior to introduction of the Chemical bank i i agents These patenis teach methods for Larger volhmes of gas have only small effects in obtain te.rmmmg Whether. i reserve 18 i Wet or l Wet and ing further improvement. Thus, the previously injected dlsclose the condltlons under whlch Weitilbmty revertal gas fills and occupies reservoir pore space thereby causing i i s 2125:3 33 jg i gg g sg zg g fg fizzi g improved distribution of the chemical solution, bringing o t e same di cuties arise, rornt e stan point 0 0p- 00 mg proce ures. or examp e, W ere 01 1s recovere by a wettability reversal method Such as disclosed i from Oil Wet or neutral wettability to water Wet is used in either of the two abovementioned patents, the flood bank 7 Volumes of at East about 1 or 2 P of the P actually has no better displacement and sweep efliciency than is experienced in ordinary Waterflooding of a watervolume to be flooded or contacted. Volumes as high as 10 percent or more of the conformable pore volume may be used. However, in the majority of cases, no advantage is to be gained by using total chemical slug volumes in excess of about 10 percent of the pore volume to be contacted. Usually, total chemical slug volumes of from about 2 to 10 percent are preferred. The concentration of chemical or chemicals in this bank likewise may vary. Generally, such concentrations of chemical may range from about 0.05 to about 2.0 molar. As examples of chemicals suitable for converting oil-wet to water-wet formations there may be mentioned the alkali metal sulfides, carbonates, and phosphates, such as sodium sulfide, ammonium sulfide, sodium carbonate, ammonium carbonate, sodium hydrogen phosphate, sodium tripolyphosphate, trisodium phosphate, ammonium phosphate, and ammonium hydrogen phosphate. Other chemicals such as sodium chloride and sodium hydroxide have been used for this purpose and in this connection it is to be understood that the term wettability reversal chemical, or equivalent designation, as used throughout the present description and claims is intended to refer to the abovenamed compounds or mixtures of two or more thereof, as well as other such materials used for this purpose and currently known to those skilled in this art.

When the slug of wettability reversal chemical has been placed in the oil-wet or neutral wettability reservoir by introduction through an injection well extending into said reservoir, it is propagated through the formation to the producing well(s), for example, by the simultaneous or alternate injection of gas and water. In terms of hydrosodium tripolyphosphate 0.4 molar in carbonate and 0.1 molar in phosphate, is used in Cases 2, 3, and 4, as shown in the table below. In all cases where the solution of wettability reversal chemical was used, it was injected in an amount corresponding to about 5 percent of the conformable pore volume. In Case 1, the saturated core is subjected to ordinary waterflooding until water breakthrough occurs. In Case 2, the solution of wettability chemical is injected until breakthrough after which water is introduced to force the slu of chemical completely through the core until it likewise breaks through. In Case 3, the wettability of the sandstone core is altered from oil wet to water wet by injection of the solution of the wettability reversal chemical until breakthrough thereof and thereafter is followed by natural gas-water (alternate) injection until the latter system breaks through, The gas slugs are approximately 5 percent HPV and the water is injected in amounts of about 10 percent HPV until breakthrough. The last case employs an embodiment of the present invention wherein the oil-wet saturated sandstone core is first injected with alternate slugs of natural gas and ammonium mono-hydrogen, or the phosphate solution, until breakthrough. Next the resulting bank of gas and chemical solution is driven through the core by means of alternate injections of natural gas and water, the total volume of gas and water thus introduced, amounting to about 35 percent of the HPV. The results obtained under these various conditions are set forth in the table below:

TABLE Case 1 Case 2 S Inj. Mobility Cumu. Sn, Inj. Mobility Cumu. Per- Pore Ratio Time Per- Pore Ratio Time cent V cent 01 Initial 90 0 0 90 0 0 Breakthrough... l 29 1 Porn Volume In] 3 Pore Volume Inj wettability Alteration.

G as Water Injection Combination of wettability Alteration and Gas-Water Injection Case 3 Case 4 S u Inj. Mobility Cumu. Sn Inj. Mobility Cumu. Per- Pore Ratio Time Per- Pore Ratio Time cent Vol. cent V01.

Initial 90 0 0 90 0 0 Breakthrough 1 Pore Volume Inj. 3 Pore Volume 111 Wettability Alteration Gas-Water Injection Combination of wettability Alteration and Gas-Water Injection 18 .96 ..1875 1.l

carbon pore volume (HPV) the volume of water employed may range from about 1 to 4 volumes per volume of gas. However, beneficial results can be achieved with only small amounts of gas, e.g., 2 percent HPV. When these fluids are injected alternately, the gas should not be injected in amounts in excess of about 5 percent HPV and the water not in excess of about 10 percent HPV. While I ordinarily prefer to use natural gas, others such as flue gas, air, and the like, may be employed. Air is sometimes preferred instead of natural gas, flue gas, etc., because of its relatively low solubility in crude oil. Any gas may be used that is substantially inert with respect to the crude oil and to the well equipment.

The advantages of the process of my invention are further illustrated by the following specific example:

EXAMPLE Four Torpedo sandstone cores, 8.5 inches by 2 inches are each saturated with a crude oil having a viscosity of 1.4 cps. The resulting oil-wet cores have an initial oil saturation of 90 percent and a connate Water saturation of 10 percent. A 0.5 molar solution of wettability reversal chemical, e.g., a mixture Of ammonium carbonate and From the above information, it will be seen that the process of my invention (Cases 3 and 4) has a number of important advantages. First, the residual oil saturation (S of 18 to 19 percent after treatment represents an improved recovery over the other two procedures used. The method employed in Case 3, using a wettability a1- teration flood followed by gas-water injection, almost equaled Case 4 in oil recovery; however, it will be noted that Case 3 required injection of 1.36 pore volumes of flooding components, whereas Case 4 required injection of only .96 pore volume to secure the improved recovery. Where gas is injected into the reservoir prior to, alternately, or simultaneously with the chemical bank, it has been my observation that this technique with the same chemical injection requirements will increase recovery by at least 10 percent.

It will likewise be seen that in Case 4, the mobility ratio is more favorable than in any other of the three cases investigated and the flood life is also shorter than any of the other cases when taking into consideration the relatively low injection volume required to complete this flooding operation. Thus, in the waterflood operation (Case 2), it will be noted that while the time required for breakthrough is slightly more than one-third that required for breakthrough in Case 4, the residual oil saturation in Case 2 is relatively higher, i.e., 29 percent, and the mobility ratio is substantially twice that of the system in Case 4. The flood life of any project is always a very important factor and any means by which this period can be shortened is highly desirable since it is now a fairly wellestablished rule of thumb that in a flooding project for each year of operation of one injection well and one producing well, the cost is about $5,000.

It will be apparent that the principle of my invention is applicable to a wide variety of oil-Wet and neutral wettability reservoirs to achieve high oil recoveries in a shorter period of time for less operating expense and investment cost than is required by other improved water flooding methods to obtain comparable recoveries. Accordingly, any flooding procedure involving the use of an initial bank of wettability reversal chemical followed by gas-water injection, or the equivalent, wherein the chemical bank is injected before, after, or during the introduction of a gas slug into the reservoir to improve the efliciency of an oil recovery process, is contemplated as lying within the scope of my invention.

The term reservoir, as used in the present claims is intended to refer only to oil-wet and/or neutral wettability reservoirs.

I claim:

1. In a method for the recovery of petroleum from an oil-wet and/or neutral wettability reservoir thereof having an injection well and a producing well extending into said reservoir wherein an initial bank of a solution of wettability reversal chemical is introduced into said reservoir via said injection well and thereafter propelled through said reservoir toward said producing well by means of a fluid drive agent,

the improvement which comprises introducing a gas into said reservoir via said injection well in conjunction with said chemical.

2. In a method for the recovery of petroleum from an oil-wet and/ or neutral wettability reservoir thereof having an injection well and a producing well extending into said reservoir wherein an initial bank of a solution of wettability reversal chemical is introduced into said reservoir via said injection well and thereafter propelled through said reservoir toward said producing well by means of a fluid drive agent,

the improvement which comprises introducing a gas into said reservoir in the vicinity of said injection well prior to the injection of said initial bank.

3. The method of claim 1 wherein said gas and chemical solution are injected as alternate slugs.

4. The method of claim 1 wherein said gas and chemical solution are injected simultaneously.

5. The method of claim 1 wherein said fluid drive agent is composed of alternate slugs of gas and water.

6. T he method of claim 1 wherein said fluid drive agent is composed of gas and water which are injected simultaneously into said reservoir.

7. The method of claim 1 wherein the solution of wettability reversal chemical injected amounts to from about 2 to about 10 percent of the pore volume to be flooded and the gas used in conjunction with said solution amounts to not more than about 20 percent of the pore volume to be flooded.

8. The method of claim 7 wherein the concentration of the chemical in said solution ranges from about 0.1 to about 2.0 molar.

9. The method of claim 8 wherein said chemical is selected from the group consisting of sodium sulfide, ammonium sulfide, ammonium monohydrogen orthophosphate, sodium tripolyphosphate, ammonium di-hydrogen orthophosphate, sodium orthophosphate, sodium monohydrogen orthophosphate, sodium di-hydrogen orthophosphate, sodium pyrophosphate, sodium hydroxide and sodium chloride.

10. The method of claim 7 wherein said fluid drive agent is composed of gas and water in a ratio of about 1:2 to about 1:5, respectively.

11. The method of claim 1 in which gas is injected into said reservoir via said injection well in conjunction with both the initial bank of wettability reversal chemical and with the fluid drive agent.

References Cited UNITED STATES PATENTS 2,800,962 7/1957 Garst 166-9 2,875,831 3/1959 Martin et al. l669 3,191,676 6/1965 Froning l669 3,203,480 8/1965 Froning l669 X 3,244,228 4/1966 Parrish 166-9 3,245,467 4/1966 Fitch l669 3,258,071 6/1966 Chen Yu Shen l66-9 STEPHEN J. NOVOSAD, Primary Examiner. 

